Continuously variable valve lift systems are known in the engine arts. See, for example, the system disclosed in US Patent Application Publication No. 2007/0125329, published Jun. 7, 2007 and incorporated herein by reference. Such a system incorporates a crank mechanism for selective continuous variation of the contact point of a special rocker subassembly (RS) with the engine camshaft to vary the angular rotational motion of the RS. The RS is positioned between the engine camshaft and the valvetrain's roller finger follower (RFF). The RS includes a secondary cam surface followed by the RFF. Varying the contact point of the RS on the camshaft has the effect of varying the lift and the opening and closing timing of the associated engine combustion valve. For a cylinder having dual intake or dual exhaust valves, the RS comprises a wide secondary cam surface that is followed identically by the RFF for each valve.
Variable valve activation/deactivation (WA) systems are also known in the engine arts. See, for example, U.S. Pat. No. 6,321,704 that discloses a deactivating hydraulic lash adjuster (DHLA), and U.S. Pat. No. 7,093,572 that discloses a deactivating roller finger follower (DRRF), both of which are incorporated herein by reference. Each of these prevents the rotary motion of the camshaft lobe from being translated into reciprocal motion of the associated valve stem by absorbing the equivalent motion within itself (“lost motion”). Thus the valve is “deactivated” and prevented from opening on schedule.
For gasoline engines, compromises inherent with fixed valve lift and event timing of a conventional valve train have prompted engine designers to consider Continuously Variable Valve Lift (CVVL) systems for more flexible air flow control optimized for each engine load and speed condition. In recent years, some relatively basic forms of CVVL have been introduced into production engines. Greater performance and drivability expectations of customers, more stringent emission regulations set by government legislators, and the mutual desire for higher fuel economy are increasingly at odds. As a solution, some vehicle manufacturing companies are considering large-scale application of higher function CVVL mechanisms in their next generation vehicles, mainly to improve fuel economy, by reducing pumping loss, and cold start combustion stability, with increased cylinder air flow tumble motion. However, the CVVL engine has two critical engineering challenges for turbulence (swirl or tumble) enhancement and cylinder by cylinder valve lift variation, which requires combustion chamber masking for tumble enhancement and costly select fit of output rocker cam or roller finger followers for CVVL.
When applying a prior art CVVL system, current engine combustion strategies allow the intake valve to open from zero to full lift, as described above. However, the use of variable lift mechanisms has been limited on dual intake valves to the same lift on both valves of each cylinder, which cannot provide any in-cylinder air flow turbulence enhancement.
What is needed in the art is a CVVL system wherein in-cylinder turbulence is enhanced during variable-lift operation of an internal combustion engine, and especially under low lift flow conditions.
It is a principal object of the present invention to provide increased in-cylinder turbulence during variable-lift operation of an internal combustion engine.